Device and method for measuring a force component or torque component

ABSTRACT

A device and method for measuring at least one of a force component and a torque component. The device includes a deformation member, for measuring at least one of a force component and torque component, a separate measuring element, configured to measure at least one force component, and an electronics unit, connected to the measuring element configured to evaluate a measuring signal of the measuring element. The deformation member includes a base part and at least one tongue movable with respect to the base part. The base part is arranged so that a gap between the measuring element and the tongue has a gap width variable in response to the force component introduced onto the deformation member. The measuring element is configured to convert a change in the gap width into a measuring signal. The method includes the step of changing the gap width between the tongue and the measuring element by introducing the force component into the deformation member. The method further includes the step of detecting the change in the gap width by the measuring element. The method further includes the step of directing the measuring signal by the measuring element to the electronics unit for further processing as a function of the change in the gap width.

This application is a 371 of PCT/DE02/04339 Nov. 27, 2002.

FIELD OF THE INVENTION

The present invention relates to a device and a method for measuring aforce component or torque component. In particular, the device and themethod are suitable for determining the weight of an object.

BACKGROUND INFORMATION

A multitude of devices and methods are conventional for measuring forcecomponents, the devices and methods using various physical effects toindicate the solution of the force measurement, and the force componentsmeasured in the devices and methods being converted to a measuringsignal that can be analyzed in a simple manner. An example of this is atensile/compressive force sensor, which functions according to theprincipal of strain gauges. Strain gauges are attached to aforce-absorbing element and connected to a full-bridge circuit, whichincreases its electrical resistance in response to the action of a forceand generates a bridge output voltage proportional to the measuredvariable.

However, in order to attain an optimum measuring accuracy, no transverseforces or torques may be applied to the sensor, i.e., the force may onlybe introduced in a specific direction. In addition, it is expensive tomanufacture such a force sensor, since the strain gauges and theremaining components of the force sensor must be assembled to form acomplex module.

It is an object of the present invention to provide a device and amethod for measuring a force component or torque component, where theforce components may be measured simply, inexpensively, and reliably.

SUMMARY

By designing a deformation member to have a base part and at least onetongue that is movable with respect to the base part, a gap is formedwhose width may be varied by introducing a force component. A measuringelement, which may function in a contactless manner, converts the changein the gap width to a measuring signal.

At least one guide device may be provided, which limits the mobility ofthe tongue in at least one direction, so that the tongue does not haveunlimited mobility. On one hand, the guide device or guide devicesprevent the tongue from being moved in an unsuitable manner with respectto the base part, by several, introduced force components or introduced,force components of different orientation, through which the measuringresult is invalidated. On the other hand, the guide device or devicesprevent the measuring element from being able to be ruined. Therefore,the relative movement of the tongue with respect to the base part is aguided movement, which provides an increased level of safety againstmechanical destruction of the device.

Together with the electronics unit, the deformation member and themeasuring element may take the form of separate modules, which meansthat separate manufacturing of the modules is possible. This allows themanufacturing operations of the two modules to be optimized separatelyfrom each other, and allows only the final assembly, i.e., theinstallation of the module having the measuring element and theelectronics unit in the deformation member, to be accomplished as ajoint working step.

In order to achieve an especially compact design and protect theelectronics unit and the measuring element from mechanical damage, themeasuring element and the electronics unit are positioned inside thedeformation member. In this manner, the deformation member also assumesthe function of a housing, in addition to providing a reference surfacefor measuring the displacement of the tongue with respect to the basepart.

In an exemplary embodiment of the present invention the measuringelement is an integral component of the electronics unit and takes theform of, e.g., a printed inductance coil with or without a core, on aprinted circuit board made of plastic, ceramic, etc.

A one-piece construction formed, for example, by primary shaping or bymilling out the receptacles for the module having the measuring elementand the electronics unit increases the strength of the deformationmember, and manufacturing it with the aid of a reshaping methodparticularly reduces the number of working steps and, thus,manufacturing time and costs. Furthermore, the one-piece manufacture ofthe deformation member from the base part and the tongue allows thepossibility of utilizing the elastic characteristics of thedeformation-member material for the elastic recovery of the tongue, whenthe force component or force components are no longer introduced.

In order to be able to realize a low wall thickness of the housing, evenin the case of high loads, the deformation member is made of metal, suchas steel or stainless steel, the elastic qualities of a metallicmaterial being provided for the return movement of the tongue into thestarting position.

The measuring element may take the form of a capacitor, inductance coil,piezoelectric element, or Hall-effect element and functions on acapacitive, inductive, piezoelectric, or magneto-elastic basis. The gapis compressed when a force is introduced onto the tongue or thedeformation member, the motion being converted to an electrical signalproportional to the introduced force. The wear of the measuring elementor the device is practically eliminated and simple recalibration isallowed because of the contactless measurement.

In an exemplary embodiment of the present invention, the guide device ordevices is made of a bolt connected to the base part, or a spacebushing, such as a round bolt or a round space bushing having a T-shapedcross section, and of a passage, which is positioned or formed at thetongue or the base part, and through which the bolt at least partiallypasses. The fact that the guide device takes the form of a bolt allowsmovement to be limited to a single movement direction, namely parallelto the longitudinal extension of the bolt, which means that it ispossible to precisely measure the specific force component as a functionof the orientation of the guide device. The direction of the forcecomponent may be selected and exactly determined as a function of theorientation of the guide device or the bolt, since no movements, or onlyslight movements, deviating from a movement perpendicular to the basepart are allowed. In particular, no flexural torques are generated,which easily result in damage to the device and falsification of themeasuring results.

A device is provided for limiting the movement of the tongue in thedirection of the measuring element or the base part, in order thatoverload protection of the measuring element and the entire device isset up. In this manner, forces lying above the established measuringrange are intercepted without destroying the device or the sensor.

Depending on the structural form of the tongue or the base part, it isprovided that the gap width be adjusted to the measuring range, in orderto allow use of it for various measuring purposes. In the case of amultipiece construction of the base part and tongue, this may beachieved by increasing the distance between the tongue and the base partwith the aid of distance pieces. In the case of a one-piececonstruction, the tongue may be plastically deformed to increase the gapwidth, or the gap may be permanently enlarged by machining it. Areduction in the gap width is possible, for example, using separatecomponents that are attachable to the tongue. For example, a plate maybe cemented on or a set screw may be adjusted.

In an exemplary embodiment of the present invention, the flexuralstiffness of the tongue may be changed by weakening the material orintroducing bores having an adjusted diameter at various locations.

Specularly symmetric configurations of two tongues, which may have endspointing in directions opposite to one another, allow generated torquesto be measured in the event of a non-uniform load, e.g., a seat rail,and allow the corrected weight to be determined with the aid ofmathematical adjustment. In addition, force-introduction ranges areprovided for precisely introducing the force into the tongue, so thatthe measuring element or measuring elements may be precisely assigned tothe location of the tongue displacement. This means that the measuringaccuracy is increased.

In particular, in the case of a specularly symmetric configuration ofthe force-introduction regions, which may take the form of point-shapedprojections or recesses having a small surface area, differentdisplacements are metrologically determined in addition to introducedtorques being mechanically compensated for, in that eachforce-introduction region is assigned a measuring element, so that thedistribution of forces introduced into the tongue or the tongues may bedetermined. This is accomplished, for example, by a star-shapedconfiguration of the tongues or an arrangement of two measuring elementson the diametrically opposed corners of the tongue ends. When thetongues are positioned oppositely to each other, a rectangular or squareformation of the measuring elements and the force-introduction regionsis formed, by which the effective weight may easily be determinedwithout interfering torques being generated or having to be considered.

In an exemplary embodiment of the method of the present invention formeasuring a force component or torque component, such as the weight, thegap width is changed by introducing the force components onto thetongue, the measuring element detects the change in the gap width, and ameasuring signal is routed to the electronics unit for furtherprocessing as a function of the change in the gap width. The directconversion of the movement into an electrical signal proportional to thegap width and, thus, to the introduced force allows the force componentto be determined in a simple manner and the measuring signal to beeasily processed further.

The device may be used to detect the seat-occupancy and/or the occupantweight in a motor vehicle, through which, in particular, the airbagactivation may be controlled and/or the fill level of the airbag may beadjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary embodiment of thedevice;

FIG. 2 a rear view of the device according to FIG. 1;

FIG. 3 is a plan view of the device according to FIG. 1;

FIG. 4 is a side view of another exemplary embodiment of the device;

FIG. 5 is a sectional view in the drawing plane of the device accordingto FIG. 4;

FIG. 6 is a plan view of the device according to FIG. 4;

FIG. 7 is a sectional view perpendicular to the drawing plane, of thedevice according to FIG. 4;

FIG. 8 is a sectional view perpendicular to the drawing plane, of thedevice according to FIG. 4; and

FIG. 9 a side view of the device according to FIG. 4.

DETAILED DESCRIPTION

FIG. 1 is a sectional view of an exemplary embodiment of device 1 formeasuring a force component or torque component, on which a deformationmember made of a base part 3 and a tongue 2 movable with respect to itis constructed. In the present example, the deformation member is formedin one piece, i.e., base part 3 and tongue 2 movable with respect to itwere manufactured from a semifinished material in a primary shapingprocess or reshaping process, or by machining, or they are integrallyconnected to each other. An opening for accommodating a measuring unit 5and an electronics unit 6 is formed inside the deformation member, sothat the deformation member additionally constitutes the housing formeasuring element 5 and electronics unit 6 formed together with it as amodule. Formed between tongue 2 and base part 3 is a gap 4, whose widthchanges as a function of a force introduced in the direction of thearrow or the direction opposite to that of the arrow.

Measuring element 5, e.g., an inductance coil with or without a core, aHall-effect element, a capacitor, or a similar, contactless measuringelement, measures the decrease or the increase in the gap width andtransmits the measuring signal to electronics unit 6. The measuringsignal is directed from electronics unit 6 to an interface for furtherprocessing, which is not designated in any more detail.

Shown in FIG. 2 is a rear view of device 1, in light of which theformation of gap 4 between base part 3 and tongue 2 may be recognized.The gap width changes by introducing a force component in the ydirection or the direction opposite to the y direction, and acorresponding measuring signal may be detected.

A bolt 7 is provided for limiting the movement of tongue 2 in the ydirection, the bolt being able to take, for example, the form of awelded bolt or a screw and accordingly being integrally connected tobase part 3 or connected to it in a form-locked manner. Formed on theupper face of bolt 7 is a mushroom-shaped, flattened region, whichlimits the movement of tongue 2 in the y direction, so that it is notpossible to widen gap 4 beyond an allowable or predetermined dimension.In this context, bolt 7 traverses a passage 8, which is formed by lugsthat-are formed on tongue 2.

This becomes clear from FIG. 3, in which it is illustrated that twoprotuberances are formed on the side of tongue 2, the protuberanceshaving passages 8 through which the screws or welded bolts 7 are guided.These limit the possible movement of tongue 2 in the x, y, and zdirections, base part 3 limiting the movement of tongue 2 in thenegative y direction. This protects the device from overload, i.e., theforces that lie over the measuring range or point in an undesirabledirection are intercepted without destroying the complete device ormeasuring element 5. An additional limitation to the movement of tongue2 is provided in the negative y direction, as well, in order to definethe maximum measuring range, if a limit stop is not desired on base part3. Such a limitation may be formed by set screws, which means that thepath of tongue 2 is mechanically limited in all directions.

This allows the device to be designed for any measuring ranges,independently of the electronics, by changing the geometry, in that,e.g., threaded bolt 7 is screwed in or screwed out. The same applies toadjusting the device for limiting the movement of tongue 2 in thedirection of base part 3.

The modular construction of the deformation member, and of electronicsunit 6 together with measuring element 5, which shown in the figures,allows separate manufacturing to be carried out, the interconnection ofthe two modules representing the only common operation. Measuringelement 5 or the measuring pick-up may be an integrated part ofelectronics unit 6, which means that the set-up inside the deformationmember is further simplified. According to the exemplary embodiment, thedevice only measures the forces in the y direction, since the gapdistance is changed, so that lateral interference forces in the x and zdirections are not detected or measured, which means that the forcecomponent in the predetermined direction is precisely measured.

As an alternative to the represented, one-piece construction, tongue 2is, for example, flexibly mounted to base part 3 via a hinge andoptionally loaded by a spring, in order to move tongue 2 back into thestarting position after removal of the load.

The device may be provided for detecting the seat occupancy of a motorvehicle, which means that unnecessary activation of an airbag isprevented. The occupant weight may also be determined by incorporatingthe device or a plurality of devices under the seat, which means that ispossible to control the fill level of the airbag. The heavier theoccupant, the greater the amount of air required in the airbag to ensurethat the occupant is safely caught. The fill level of the airbag may beadjusted, for example, by firing the airbag in steps. Conversely, areduced fill level is needed when the occupant is very light.

Another exemplary embodiment of the device is illustrated in FIG. 4,where two flexible tongues 2 are formed on base part 3, symmetrically tothe center line. Consequently, two gaps 4 are formed between movabletongues 2 and base part 3, the gaps being able to be changed byintroducing a force, and, in the exemplary embodiment represented, theforce being introduced by a seat rail 50 of a motor-vehicle seat. Assoon as an occupant sits on the motor-vehicle seat, forces pass throughfastening points A to seat rail 50, pass through seat rail 50 to a solidplate 40, and are transmitted to movable tongues 2. Plate 40 is formedindependently of base part 3 and movable tongues 2 and has a milledcut-out, so that the forces absorbed by seat rail 50 are onlytransmitted to tongues 2 at the outer regions of plate 40. This isexplained in detail later.

The change is the gap width is then measured in a manner as describedabove, and then converted into an electrical signal that is analyzed.

A sectional view of FIG. 4 is represented in FIG. 5, where a spacer tube30 situated above tongues 2 in the center of base part 3 is clearlyseen. As indicated in FIG. 4, spacer tube 30 is attached to the bodyfloor or another rigid base, via a centrally situated screw passingthrough a central bore, and is therefore fixed in relation to base part3. At its top end, spacer tube 30 has a T-shaped collar whose bottomedge is a specific distance from the upper edge of plate 40. TheT-shaped collar forms a limit stop for plate 40, if a movement occurs inthe direction of the T-shaped collar in the case of an accident. Inreference to the coordinate system used in FIGS. 1 through 3, this is amovement in the positive y direction. The maximum deflection capabilityof movable tongues 2 in the negative y direction is given by the gapwidth; upon reaching and exceeding the fixed measuring range, tongue 2rests on base part 3 and prevents the measuring element from beingdestroyed.

FIG. 6 is a plan view of the device according to FIG. 4, where seat rail50 has been removed so that plate 40 may be seen. Cut-outs 41 areintroduced in plate 40 to the right and left of the center line, thecut-outs allowing, on one hand, a view of underlying tongue 2 andproducing, on the other hand, force-introduction regions 42. Sketched inthe views of FIGS. 4 and 5 is a ridge, which is parallel to the lateraledges of plate 40 and interrupted by recesses 41, so that rectangularforce-introduction regions 42 acting on the ends of the tongues areformed at all four corners of plate 40. In response to the introductionof a force onto plate 40, the force is distributed to all four cornersof the plate and introduced via force-introduction regions 42 to thecorners of the two diametrically opposed tongues 2. Subsequentelectronic compensation is allowed in this manner. The interpositioningof plate 40 also allows, e.g., seat rail 50 to be attached more easily,since plate 40 is solid and therefore offers good possibilities forattachment.

In addition, bores 20 are illustrated in FIG. 6, which are formed inmovable tongue 2 and result in the weakening of the material and,therefore, a reduction in the flexural strength of elastic tongue 2,which is integrally formed in the present exemplary embodiment.Adjustments to the measuring range may be made by changing the numberand configuration of bores 20, or by increasing the bore cross-section.

Shown in FIG. 7 is a view of a section perpendicular to the plane of thedrawing, the section being taken through the lower region of plate 40,so that force-introduction regions 42 are covered. Accordingly, theseare drawn with hatching in FIG. 7; the rest of the view shows elastictongues 2, as well as the bores situated in tongue 2. Here, it is clearthat force-introduction regions 42 are arranged in a specularlysymmetric manner, so that it is possible to electronically compensatefor the introduced forces while preventing undesirable torques.

FIG. 8 shows a view of a section perpendicular to the plane of thedrawing, through gap 4, so that the center ridge of base part 3 isrepresented with hatching. From FIG. 8, it becomes clear that ameasuring element 5 having an active surface sits underneath eachforce-introduction region 42, the measuring element detecting the changein the gap width and transmitting it to an electronics unit 6, whichconverts and evaluates the corresponding signals. As an alternative tothe represented design having four separate measuring units, it isprovided that these be positioned in one piece on a printed circuitboard, the measuring elements being manufactured as, for example,printed inductance coils that may be on the printed circuit board(plastic, ceramic, etc.). Therefore, the measuring element andelectronics unit are integrated to form a module, which means thatmanufacturing and assembly may be simplified.

Illustrated in FIG. 9 is a side view of FIG. 4, from which theattachment of the measuring elements and electronics unit 6 belowtongues 2 is shown, as well as gap 4 formed by tongues 2.

As is clear from FIGS. 4 through 9, the deformation member may me madeup of several separate pieces, e.g., a plate 40, as well as a base part3 and elastic tongues 2 formed on it. As an alternative to a two-piecedesign, the tongue or tongues 2 may also be manufactured separately frombase part 3 and connected by the central fastening screw within thescope of assembly. In contrast to the represented design, it is alsopossible that no base-part 3 stop face parallel to tongue 2 is formed,but that the gap is directly formed between a separate measuring element5 and tongue 2, a limitation in the negative y direction being producedby a separate device, for example, a separate limit stop.

The deformation member may be made of metal and and may be fixed to thevehicle floor by a central screw. The fastening screw fixes base part 3having integrally formed tongue 2 to the vehicle floor, via spacer tube30, and attaches plate 40 to tongues 2.

1. A device for measuring at least one of a force component and a torquecomponent, comprising: a deformation member; a separate measuringelement configured to measure at least one force component; and anelectronics unit connected to the measuring element configured toevaluate a measuring signal of the measuring element; wherein thedeformation member includes a substantially fixed base part and at leastone tongue movable with respect to the base part, the base part arrangedso that a gap between the base part and the tongue has a gap widthvariable in response to the force component introduced onto thedeformation member, the measuring element configured to convert a changein the gap width into a measuring signal.
 2. The device as claimed inclaim 1, wherein the deformation member, the measuring element and theelectronics unit are separate modules.
 3. The device as claimed in claim1, wherein the measuring element and the electronics unit are at leastpartially surrounded by the deformation member.
 4. The device as claimedin claim 1, wherein the measuring element is integral with theelectronics unit.
 5. The device as claimed in claim 1, wherein thedeformation member is formed in one piece from the base part and thetongue.
 6. The device as claimed in claim 1, wherein the deformationmember is made of metal.
 7. The device as claimed in claim 1, whereinthe deformation member is made of at least one of steel and stainlesssteel.
 8. The device as claimed in claim 1, wherein the measuringelement is configured to operate capacitively, inductively,piezoelectrically, and magnetoelastically.
 9. The device as claimed inclaim 8, wherein the measuring element includes one of a capacitor, aninductance coil, a piezoelectric element, and a Hall-effect element. 10.The device as claimed in claim 1, wherein force-introduction regions arearranged to introduce the force component into the tongues in a precisemanner.
 11. The device as claimed in claim 10, wherein theforce-introduction regions are positioned in mirror symmetry to eachother.
 12. The device as claimed in claim 10, wherein eachforce-introduction region is assigned one measuring element.
 13. Thedevice as claimed in claim 1, wherein the force component includes aweight of a motor vehicle seat occupant.
 14. The device as claimed inclaim 1, wherein the device is configured at least one of to detect seatoccupancy and to determine occupant weight in a motor vehicle.
 15. Adevice for measuring at least one of a force component and a torquecomponent, comprising: a deformation member; a separate measuringelement configured to measure at least one force component; anelectronics unit connected to the measuring element configured toevaluate a measuring signal of the measuring element; wherein thedeformation member includes a base part and at least one tongue movablewith respect to the base part, the base part arranged so that a gapbetween the measuring element and the tongue has a gap width variable inresponse to the force component introduced onto the deformation member,the measuring element configured to convert a change in the gap widthinto a measuring signal; and at least one guide device configured tolimit mobility of the tongue in at least one direction.
 16. The deviceas claimed in claim 15, wherein the guide device includes a bolt and apassage, said passage at least one of positioned and formed on thetongue, said bolt connected to the base part, positioned perpendicularlyto the base part, and at least partially passing through the passage.17. The device as claimed in claim 15, wherein the guide device isconfigured to limit movement of the tongue at least one of in adirection of the measuring element and in a direction away from themeasuring element.
 18. The device as claimed in claim 17, wherein thelimit device is arranged on one of the deformation member, the base partand the tongue.
 19. A device for measuring at least one of a forcecomponent and a torque component, comprising: a deformation member; aseparate measuring element configured to measure at least one forcecomponent; and an electronics unit connected to the measuring elementconfigured to evaluate a measuring signal of the measuring element;wherein the deformation member includes a base part and at least onetongue movable with respect to the base part, the base part arranged sothat a gap between the measuring element and the tongue has a gap widthvariable in response to the force component introduced onto thedeformation member, the measuring element configured to convert a changein the gap width into a measuring signal, wherein at least one of thegap width and a flexural stiffness of the tongue is adjustable to ameasuring range.
 20. The device as claimed in claim 1, wherein twotongues are positioned on the base part in mirror symmetry to eachother.
 21. The device as claimed in claim 20, wherein ends of thetongues point in opposite directions.
 22. A method for measuring atleast one of a force component and torque component in accordance with adevice including a deformation member, a separate measuring elementconfigured to measure at least one force component and an electronicsunit connected to the measuring element configured to evaluate ameasuring signal of the measuring element, the deformation memberincluding a substantially fixed base part and at least one tonguemovable with respect to the base part, the base part arranged so that agap between the base part and the tongue having a gap width variable inresponse to the force component introduced onto the deformation member,the measuring element configured to convert a change in the gap widthinto a measuring signal, comprising: changing the gap width between thetongue and the base part by introducing the force component into thedeformation member; detecting the change in the gap width by themeasuring element; and directing the measuring signal by the measuringelement to the electronics unit for further processing as a function ofthe change in the gap width.
 23. The method as claimed in claim 22,further comprising the step of determining torque from a load acting onat least two tongues.
 24. The method as claimed in claim 23, furthercomprising the step of correcting measured force by arithmeticadjustment of an ascertained torque.
 25. The method as claimed in claim22, further comprising the step of at least one of detecting seatoccupancy and determining occupant height in a motor vehicle.
 26. Adevice for measuring at least one of a force component and a torquecomponent, comprising: a deformation member; a separate measuringelement configured to measure at least one force component; and anelectronics unit connected to the measuring element configured toevaluate a measuring signal of the measuring element; wherein thedeformation member includes a base part and at least one tongue movablewith respect to the base part, wherein the measuring element ispositioned in proximity to one of the base part and the at least onetongue, and wherein a gap defined by the measuring element on a firstside and the tongue on a second side has a gap width variable inresponse to the force component introduced onto the deformation member,the measuring element configured to convert a change in the gap widthinto a measuring signal.